African swine fever virus multigene family 360 and 530 genes are novel macrophage host range determinants

Pathogenic African swine fever virus (ASFV) isolates primarily target cells of the mononuclear-phagocytic system in infected swine and replicate effic iently in primary macrophage cell cultures in vitro. ASFVs can, however, be adapted to grow in monkey cell lines. Characterization of two cell culture -adapted viruses, MS16 and BA71V, revealed that neither virus replicated in macrophage cell cultures. Cell viability experiments and ultrastructural a nalysis showed that infection with these viruses resulted in early macropha ge cell death, which occurred prior to viral progeny production. Genomic co smid clones from pathogenic ASFV isolate E70 were used in marker rescue exp eriments to identify sequences capable of restoring MS16 and BA71V growth i n macrophage cell cultures. A cosmid clone representing a 38-kbp region at the left terminus of the genome completely restored the growth of both viru ses. In subsequent fine-mapping experiments, an 11-kbp subclone from this r egion was sufficient for complete rescue of BA71V growth. Sequence analysis indicated that both MS16 and BA71V had significant deletions in the region containing members of multigene family 360 (MGF 360) and MGF530, Deletion of this same region from highly pathogenic ASFV isolate Pr4 significantly r educed viral growth in macrophage cell cultures. These findings indicate th at ASFV MGF360 and MGF530 genes perform an essential macrophage host range function(s) that involves promotion of infected-cell survival.